The tailgate of a conventional pickup truck is generally adapted for easy removal, for example, to facilitate the removal and loading of the contents of the truck bed. In a common arrangement, as shown in FIG. 1, a tailgate 10 is provided with a C-shaped hinge cup or hollow axle 12 that surrounds an oblong or flatted shaft 16 secured to the truck body 15, allowing the tailgate 10 to pivot about the shaft 16. When the tailgate 10 is pivoted to a releasing orientation, the shaft 16 aligns with a slot or opening 13 in the hollow axle 12, allowing the axle 12 to be pulled free from the shaft 16 for removal of the tailgate 10 from the truck body 15. While this arrangement provides for quick and easy detachment of the tailgate, the arrangement also presents a risk of theft of a tailgate that has not been locked in the closed (i.e., vertical) position.